1. Field of Invention
The invention relates to an ink jet head for printing by ejecting ink onto a print medium, and to an ink jet printer having the ink-jet head.
2. Description of Related Art
In an ink-jet printer, an ink-jet head distributes ink supplied from an ink tank to pressure chambers. The ink-jet head selectively applies pressure to each pressure chamber to eject ink through a nozzle. As a means for selectively applying pressure to the pressure chambers, an actuator unit may be used in which ceramic piezoelectric sheets are laminated.
As an example, a generally known ink-jet head has one actuator unit in which continuous flat piezoelectric sheets extending over a plurality of pressure chambers are laminated. At least one of the piezoelectric sheets is sandwiched by a common electrode which is common to many pressure chambers and is being kept at the ground potential, and many individual electrodes, i.e., driving electrodes, disposed at positions corresponding to the respective pressure chambers. When a individual electrode on one face of the sheet is set at a potential different from that of the common electrode on the other face, the part of piezoelectric sheet being sandwiched by the individual and common electrodes and polarized in its thickness, is expanded or contracted in its thickness direction as an active layer by the so-called longitudinal piezoelectric effect. This causes the volume of the corresponding pressure chamber to change, so that the ink can be ejected toward a print medium through a nozzle communicating with the pressure chamber.
In the above-described ink-jet head, to ensure good ink ejection performance, the actuator unit must be accurately positioned to a passage unit so that the individual electrodes must be at predetermined positions corresponding to the respective pressure chambers in a plan view.
Generally, in an ink-jet head such as the one described above, the passage unit in which ink passages including pressure chambers have been formed is manufactured separately from the actuator unit. The passage unit is then bonded with an adhesive to the actuator unit so that the pressure chambers are close to the actuator unit. This bonding process is done by matching a mark formed on the passage unit against a mark formed on the actuator unit.
Generally, the piezoelectric sheets of the actuator unit are manufactured through a sintering process while the passage unit is laminated with metallic sheets. Therefore, as the size of the piezoelectric sheets increases, the positional accuracy of the electrodes decreases. Thus, the longer the head is, the more difficult the positioning process is between the pressure chambers in the passage unit and the individual electrodes in the actuator unit. As a result, the manufacturing yield for the printer heads is reduced.
Furthermore, because the actuator unit it is made of ceramic, it is an expensive and very brittle component. In particular, in the actuator unit having a polygonal shape, the corners can easily brake. The breakage loss causes the manufacture cost to increase. Further, the actuator unit requires very delicate handling to ensure that a corner does not collide against another component. This makes the ink-jet head assembling difficult.